A novel method is developed to provide high-resolution, full-field retardation measurement of the liquid crystal cell using a phase shift polariscope. The phase retardation of a liquid crystal cell is influenced by its thickness, and hence an accurate measurement of the full field retardation gives the thickness distribution of the liquid crystal cell. In the phase shift polariscope, phase shift images obtained by rotating the analyzer are recorded and analyzed to obtain the phase retardation and hence the whole field thickness distribution of the liquid crystal cells. The results obtained using this method are compared with those using a commercial pointwise sensor with good agreement. The proposed method yields accurate and repeatable full-field cell gap measurement of the liquid crystal cell with a simple experimental setup.